Method of diminishing the minimum range of operation of a communication link

ABSTRACT

A portable electronic device comprises a wireless receiver unit for receiving a wireless signal from a transmitting device, the wireless receiver unit comprising an antenna receiving an electromagnetic signal and providing a received electric input signal, and a receiver providing a recovered electric signal from the received electric input signal, and an impedance matching circuit matching the electric impedance of the antenna to the receiver, the receiver comprising a gain stage comprising an Automatic Gain Control unit automatically determining an AGC-gain value for application to an AGC-input signal to provide an appropriate signal level when the level of said AGC input signal is in a range between a minimum and a maximum signal level corresponding to maximum and minimum AGC-gain values, respectively. The portable device further comprises a control unit receiving the AGC-gain value and providing a control signal depending on said AGC-gain value to the impedance matching circuit.

CROSS REFERENCE TO RELATED APPLICATIONS

This nonprovisional application claims priority under 35 U.S.C. 119(a)to Patent Application No. 11175282.0 filed in Europe, on Jul. 26, 2011and under 35 U.S.C. 119(e) to U.S. Provisional Application No.61/511,563 filed on Jul. 26, 2011. The entire contents of all of theabove applications are hereby incorporated by reference into the presentapplication.

TECHNICAL FIELD

The present application relates to wireless communication between mobiledevices, in particular to the minimum-distance problem in acommunication link. The disclosure relates specifically to a portableelectronic device comprising a wireless receiver unit for receiving awireless signal from a transmitting device, the wireless receiver unitcomprising an antenna, a receiver, and an impedance matching circuit formatching the electric impedance of the antenna to the receiver, thereceiver comprising a gain stage comprising an Automatic Gain Controlunit (AGC).

The application furthermore relates to a method of operating a wirelessreceiver unit, to the use of a portable electronic device and to acommunication system comprising a portable electronic device.

The application further relates to a data processing system comprising aprocessor and program code means for causing the processor to perform atleast some of the steps of the method and to a computer readable mediumstoring the program code means.

The disclosure may e.g. be useful in applications involving portableelectronic devices capable of establishing a wireless communication linkto other devices, e.g. listening devices, such as hearing aids.

BACKGROUND

A typical communication link has a specified maximum and minimumoperating distance between transmitter and receiver. For mobile devices,such as portable communication devices or listening devices, e.g.hearing instruments, that are adapted to communicate with each other viaa wireless link, it may happen that a transmitting device and areceiving device are located (intentionally or un-intentionally) out ofthe specified operating range.

A communication system comprising first and second communication devicescomprising a dynamic regulation scheme for adapting transmit power tothe signal quality of the link established between the devices is e.g.disclosed in EP 2 211 579 A1. In an embodiment, the system is adapted touse the dynamic power regulation to implement a partial power down ofthe system, when the two communications devices are located outside thespecified operating range (i.e. either too close to each other or toofar from each other). When the two devices are too close to each other,the receiver ‘saturates’ because it is not able to handle the receivedinput level.

US 2009/0130991 A1 describes a method of matching the input of an LNA toan antenna over a range of frequencies by maximizing field strengthusing an adjustable antenna matching network. US 2004/0080372 A1describes a high frequency amplifier for a mobile phone comprisingvariable capacitors and resistors at its input and output matchingcircuits, wherein the gain and frequency response can be automaticallytuned to the avoid impact of impedance variation of the lead frame ofthe mobile phone or resulting from the manufacturing process.

SUMMARY

The present invention may be used in connection with any wireless link,comprising an antenna for receiving an electromagnetic signal andproviding a received electric signal and a transceiver for amplifyingthe received electric signal and possibly extracting an informationsignal, e.g. an audio signal, from the received electric signal.Typically the transceiver comprises a gain stage for amplifying an inputsignal and providing an amplified output signal, but no attenuationstage for attenuating an input signal.

An object of the present application is to provide a scheme forimproving flexibility in the acceptable range of operation of a wirelesslink. A further object is to decrease a minimum operating distancebetween a transmitting and a receiving device.

Objects of the application are achieved by the invention described inthe accompanying claims and as described in the following.

A Portable Electronic Device:

In an aspect of the present application, an object of the application isachieved by a portable electronic device comprising a wireless receiverunit for receiving a wireless signal from a transmitting device, thewireless receiver unit comprising an antenna for receiving anelectromagnetic signal and providing a received electric input signal,and a receiver for providing a recovered electric signal from thereceived electric input signal, and an impedance matching circuit formatching the electric impedance of the antenna to the receiver, thereceiver comprising a gain stage comprising an Automatic Gain Controlunit for automatically determining an AGC-gain value for application toan AGC-input signal to provide an appropriate signal level of therecovered electric signal when the level of said AGC input signal is ina range between a minimum signal level and a maximum signal levelcorresponding to maximum and minimum AGC-gain values, respectively,wherein the portable electronic device further comprises a control unitreceiving said AGC-gain value and providing a control signal dependingon said AGC-gain value to said impedance matching circuit, and whereinthe control unit is adapted to change the impedance matching of theantenna to the receiver based on the control signal.

This has the advantage of enhancing the dynamic range of the wirelessreceiver, e.g. allowing a smaller minimum distance between transmitterand receiver.

In the present context, the term ‘an electromagnetic signal’ is taken tomean a wireless signal comprising an electric field component and amagnetic field component (based on electromagnetic radiation) or anelectric or magnetic field component alone (based on an electric ormagnetic coupling, respectively, between appropriate capacitive andinductive components, respectively).

The variable gain of the gain stage allows the receiver itself to setthe gain to an appropriate value, ensuring the optimum signal level forthe succeeding receiver circuits. This is known as Automatic GainControl. (AGC).

It should be understood that the purpose of the impedance matchingcircuit is to provide that the received electric signal has a levelwithin the dynamic range of the following gain stage. This is achievedby dynamically varying the degree of matching of the electric impedanceof the antenna to the receiver (gain stage), thereby leaving the signalun-attenuated (optimal match), if the level of the received electricsignal is within the dynamic range of the gain stage, and attenuate(decreased match (increased mis-match)) the signal (detune the antenna),if the level of the received electric signal is too large (i.e. so thatthe gain of the gain stage cannot be sufficiently decreased to bring thelevel of the received electric signal within the dynamic range of thegain stage). The principle of the present disclosure is schematicallyillustrated in FIG. 5.

The control signal to the impedance matching circuit (for ‘matching’ theelectric impedance of the antenna to the receiver) is thus intended tocontrol the degree of match (or mis-match) of the impedance matchingcircuit (between the antenna and receiver impedances) to allow anattenuation of the received electric signal, in case its level is largerthan the upper limit of the dynamic range of the gain stage.

In general, the gain stage is able to apply a gain G_(A) to an inputsignal between a minimum value G_(Amin) and a maximum value G_(Amax).Correspondingly, the Automatic Gain Control unit is able to apply a gainG_(AGC) to an input signal between a minimum value G_(AGCmin) and amaximum value G_(AGCmax). In a particular embodiment, the Automatic GainControl unit is adapted to amplify an input signal but not to attenuatethe input signal (i.e. G_(AGCmax)≧1). In other words, the AGC unit isnot capable of reducing the input level (only to increase it).Alternatively, the minimum gain value G_(AGCmin) of the AGC unit may be<1.

The impedance matching circuit is located between the antenna and thefirst gain stage to (if necessary) be able to attenuate the signalbefore it is fed to the gain stage.

In a particular embodiment, the control unit is adapted to decrease the(degree of) impedance matching of the impedance matching circuit whensaid AGC-gain value is below a predefined minimum threshold AGC-gainvalue (thereby decreasing the strength of the signal from the antenna).In a particular embodiment, the control unit is adapted to increase the(degree of) impedance matching of the impedance matching circuit whensaid AGC-gain value is above a predefined maximum threshold AGC-gainvalue (thereby increasing the strength of the signal from the antenna).In a particular embodiment, the Automatic Gain Control unit is adaptedto provide said AGC-gain values in steps between a minimum and a maximumvalue.

The impedance matching circuit is preferably passive. In a particularembodiment, the impedance matching circuit comprises a variablecapacitance. In a particular embodiment, the impedance matching circuitcomprises a variable resistance. In a particular embodiment, theimpedance matching circuit comprises a variable inductance. In anembodiment, the impedance matching circuit comprises one or more of avariable capacitance, a variable resistance and a variable inductance.

In general, the wireless link established by the transmitter andreceiver parts can be of any type. In a near-field communication linkfor example (e.g. an inductive link), the signal strength decreases withL³, where L is the distance between transmitter and receiver. In afar-field communication link, the signal strength correspondinglydecreases with L². In particular for a communication link based onnear-field communication (e.g. an inductive link), the signal strengthis highly dependent on the distance between transmitter and receiver.The maximum transmit power of the link determines the maximum transmitrange. If e.g. a transmitter is adapted to always work at maximum power,a very large difference between received power is experienced betweenthe maximum and the minimum range of operation.

In an embodiment, the wireless link is a link based on near-fieldcommunication, e.g. an inductive link based on an inductive couplingbetween antenna coils of the transmitter and receiver parts of the firstand second communication devices, respectively. In a particularembodiment, the antenna comprises an inductance, e.g. an inductancecoil. In a particular embodiment, the wireless link is a link based on acapacitive coupling between capacitive elements of the transmitter andreceiver parts of the first and second communication devices,respectively. In an embodiment, the antenna comprises a capacitance,e.g. a patch.

In another embodiment, the wireless link is based on far-field,electromagnetic radiation.

In an embodiment, the communication via the wireless link is arrangedaccording to a specific modulation scheme, e.g. an analogue modulationscheme, such as FM (frequency modulation) or AM (amplitude modulation)or PM (phase modulation), or a digital modulation scheme, such as ASK(amplitude shift keying), e.g. On-Off keying, FSK (frequency shiftkeying), PSK (phase shift keying) or QAM (quadrature amplitudemodulation).

In a particular embodiment, the portable electronic device is adapted toprovide that the change of the impedance matching of the antenna to thereceiver is performed in one or more steps controlled by said controlsignal from the control unit. This is e.g. relevant (to be able tosequentially attenuate electric input signal received from the antenna),in case the receiver is saturated by the two devices being located closeto each other.

In a particular embodiment, the portable electronic device comprises alistening device such as a hearing aid.

In a particular embodiment, the gain stage comprises a first, fixed(pre-amplifying) gain stage and a second, variable (AGC) gain stage.When transmitter and receiver are located at a distance below the(normal) minimum operating distance, the signal strength is too high forthe receiver's first gain stage to handle (saturation), but the firstgain stage is fixed and cannot attenuate the incoming signal. In thiscase, a detuning of the antenna (by changing the impedance matchingcircuit) as proposed by the present disclosure may bring the signalstrength into the receiver's operating range (by attenuating thesignal).

In an embodiment, the portable electronic device comprises a localenergy source, e.g. a battery, e.g. a rechargeable battery. In anembodiment, the portable electronic device is a low power device. Theterm ‘low power device’ is in the present context taken to mean a devicewhose energy budget is restricted, e.g. because it is a portable device,e.g. comprising an energy source (e.g. of limited size, e.g. with amaximum capacity of 1000 mAh, such as 500 mAh), which—without beingexchanged or recharged—is of limited duration (the limited durationbeing e.g. of the order of hours or days, e.g. max. 1 or 3 or 7 or 10days (during normal operation of the device).

In an embodiment, the portable electronic device is adapted to provide afrequency dependent gain to compensate for a hearing loss of a user. Inan embodiment, the portable electronic device comprises a signalprocessing unit for enhancing the input signals and providing aprocessed output signal. Various aspects of digital hearing aids aredescribed in [Schaub; 2008].

In an embodiment, the portable electronic device comprises an outputtransducer for converting an electric signal to a stimulus perceived bythe user as an acoustic signal. In an embodiment, the output transducercomprises a number of electrodes of a cochlear implant or a vibrator ofa bone conducting hearing device. In an embodiment, the outputtransducer comprises a receiver (speaker) for providing the stimulus asan acoustic signal to the user.

In an embodiment, the portable electronic device comprises a (possiblystandardized) electric interface (e.g. in the form of a connector) forreceiving a wired direct electric input signal from another device, e.g.a communication device or another portable electronic device.

In an embodiment, the receiver of the portable electronic devicecomprises demodulation circuitry for demodulating the received electricinput signal to provide an electric input signal representing aninformation signal (e.g. an audio signal and/or a control signal e.g.for setting an operational parameter (e.g. volume) and/or a processingparameter of the portable electronic device).

In an embodiment, the portable electronic device and/or thecommunication device comprises an electrically small antenna. An‘electrically small antenna’ is in the present context taken to meanthat the spatial extension of the antenna (e.g. the maximum physicaldimension in any direction) is much smaller than the wavelength λ_(TX)of the transmitted electric signal. In an embodiment, the spatialextension of the antenna is a factor of 10, or 50 or 100 or more, or afactor of 1 000 or more, smaller than the carrier wavelength λ_(TX) ofthe transmitted signal.

In an embodiment, the communication between the portable electronicdevice and the other device is in the base band (audio frequency range,e.g. between 0 and 20 kHz). Preferably, communication between theportable electronic device and the other device is based on some sort ofmodulation at frequencies above 100 kHz. Preferably, frequencies used toestablish communication between the portable electronic device and theother device is below 50 GHz, e.g. located in a range from 100 kHz to 50MHz (such as in the range from 1 MHz to 10 MHz), or in the range from 50MHz to 50 GHz.

In an embodiment, the portable electronic device comprises a forwardpath or signal path between an input transducer (microphone systemand/or direct electric input (e.g. a wireless receiver)) and an outputtransducer. In an embodiment, the signal processing unit is located inthe forward path. In an embodiment, the signal processing unit isadapted to provide a frequency dependent gain according to a user'sparticular needs. In an embodiment, the portable electronic devicecomprises an analysis path comprising functional components foranalyzing the input signal (e.g. determining a level, a modulation, atype of signal, an acoustic feedback estimate, etc.). In an embodiment,some or all signal processing of the analysis path and/or the signalpath is conducted in the frequency domain. In an embodiment, some or allsignal processing of the analysis path and/or the signal path isconducted in the time domain. In an embodiment, the portable electronicdevice comprises an acoustic (and/or mechanical) feedback suppressionsystem. In an embodiment, the portable electronic device furthercomprises other relevant functionality for the application in question,e.g. compression, noise reduction, etc.

In an embodiment, the portable electronic device has a maximum outerdimension of the order of 0.15 m (e.g. a handheld mobile telephone). Inan embodiment, the portable electronic device has a maximum outerdimension of the order of 0.08 m (e.g. a head set). In an embodiment,the portable electronic device has a maximum outer dimension of theorder of 0.04 m (e.g. a hearing instrument).

In an embodiment, the portable electronic device comprises a leveldetector (LD) for determining the level of an input signal (e.g. on aband level and/or of the full (wide band) signal). Level detection inhearing aids is e.g. described in WO 03/081947 A1 or U.S. Pat. No.5,144,675.

Use:

In an aspect, use of a portable communication device as described above,in the ‘detailed description of embodiments’ and in the claims, ismoreover provided. In an embodiment, use in a listening devices, such asa hearing aid or a headset, is provided.

A Method:

In an aspect, a method of operating a wireless receiver unit forreceiving a wireless signal from a transmitting device, the wirelessreceiver unit comprising an antenna for receiving an electromagneticsignal and providing a received electric input signal, and a receiverfor providing a recovered electric signal from the received electricinput signal, and an impedance matching circuit for matching theelectric impedance of the antenna to the receiver is furthermoreprovided by the present application. The method comprises

a) automatically determining an AGC-gain value in the receiver forapplication to an AGC-input signal to provide an appropriate signallevel of the recovered electric signal when the level of said AGC inputsignal is in a range between a minimum signal level and a maximum signallevel corresponding to maximum and minimum AGC-gain values,respectively;b) changing the impedance matching of the antenna to the receiver in theimpedance matching circuit based on the AGC-gain value.

It is intended that the structural features of the device describedabove, in the ‘detailed description of embodiments’ and in the claimscan be combined with the method, when appropriately substituted by acorresponding process and vice versa. Embodiments of the method have thesame advantages as the corresponding devices.

A Computer Readable Medium:

In an aspect, a tangible computer-readable medium storing a computerprogram comprising program code means for causing a data processingsystem to perform at least some (such as a majority or all) of the stepsof the method described above, in the ‘detailed description ofembodiments’ and in the claims, when said computer program is executedon the data processing system is furthermore provided by the presentapplication. In addition to being stored on a tangible medium such asdiskettes, CD-ROM-, DVD-, or hard disk media, or any other machinereadable medium, the computer program can also be transmitted via atransmission medium such as a wired or wireless link or a network, e.g.the Internet, and loaded into a data processing system for beingexecuted at a location different from that of the tangible medium.

A Data Processing System:

In an aspect, a data processing system comprising a processor andprogram code means for causing the processor to perform at least some(such as a majority or all) of the steps of the method described above,in the ‘detailed description of embodiments’ and in the claims isfurthermore provided by the present application.

A Communication System:

In a further aspect, a communication system comprising a portableelectronic device as described above, in the ‘detailed description ofembodiments’ and in the claims AND a transmitting device is furthermoreprovided, the portable electronic device and a transmitting device beingadapted to establish a wireless communication link between them at leastallowing a signal to be transmitted from the transmitting device to theportable electronic device. In an embodiment, the wireless communicationlink is one-way.

In a particular embodiment, the communication system is adapted toprovide that the wireless link is based on inductive coupling betweenrespective antenna coils of the transmitting device and the portableelectronic device.

In an embodiment, the communication link between the portable electronicdevice and the transmitting device is adapted to provide thatinformation (e.g. control and status signals, possibly audio signals)can be exchanged or forwarded from one to the other (bidirectionally).

In an embodiment, the transmitting device is an audio gateway deviceadapted for receiving a multitude of audio signals (e.g. from anentertainment device, e.g. a TV or a music player, a telephoneapparatus, e.g. a mobile telephone or a computer, e.g. a PC) and adaptedfor selecting and/or combining an appropriate one of the received audiosignals (or combination of signals) for transmission to the portableelectronic device. In an embodiment, the transmitting device is anentertainment device, e.g. comprising a TV or video display unit. In anembodiment, the system is specifically adapted for transmitting andreceiving audio via the wireless communication link.

In an embodiment, the transmitting device is another listening device.In an embodiment, the communication system comprises two listeningdevices adapted to implement a binaural listening system, e.g. abinaural hearing aid system.

Further objects of the application are achieved by the embodimentsdefined in the dependent claims and in the detailed description of theinvention.

As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well (i.e. to have the meaning “at leastone”), unless expressly stated otherwise. It will be further understoodthat the terms “includes,” “comprises,” “including,” and/or“comprising,” when used in this specification, specify the presence ofstated features, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof. It will also be understood that when an elementis referred to as being “connected” or “coupled” to another element, itcan be directly connected or coupled to the other element or interveningelements may be present, unless expressly stated otherwise. Furthermore,“connected” or “coupled” as used herein may include wirelessly connectedor coupled. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items. The steps ofany method disclosed herein do not have to be performed in the exactorder disclosed, unless expressly stated otherwise.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure will be explained more fully below in connection with apreferred embodiment and with reference to the drawings in which:

FIG. 1 shows an embodiment of a portable electronic device according tothe present application,

FIG. 2 shows two embodiments of an antenna and a variable impedancematching circuit,

FIG. 3 shows two embodiments of a variable impedance matching circuit,

FIG. 4 shows a use scenario for a communication system according to thepresent application, and

FIG. 5 illustrates an example of the effect on dynamic range of theapplication of a variable impedance matching circuit according to thepresent disclosure.

The figures are schematic and simplified for clarity, and they just showdetails which are essential to the understanding of the disclosure,while other details are left out.

Further scope of applicability of the present disclosure will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the disclosure, aregiven by way of illustration only. Other embodiments may become apparentto those skilled in the art from the following detailed description.

DETAILED DESCRIPTION OF EMBODIMENTS

The idea is to monitor the incoming signal strength on an AGC of awireless receiver and switch the tank Q to a lower value (=lesssensitive receiver) before the signal overloads the input stage of thereceiver, and, of course, reversing this step when the signal gets loweragain. In an embodiment, the AGC unit has a gain control output forcontrolling the gain of a variable amplifier. The gain control outputmay be an analogue signal or a digital signal (indicating a gain settingin steps, e.g. from GC=0 to GC=31). The larger the input signal level,the smaller gain is necessary in the variable amplifier and vice versa.The gain control output is—in addition to the variable gain unit—fed toa processing unit. If the gain control signal is below a predefinedvalue (e.g. GC≦2) corresponding to a relatively low gain setting of thevariable amplifier, e.g. and thus a relatively strong input signal), thereceiving antenna is (increasingly, e.g. in one or more steps) de-tunedto lower the signal strength. Correspondingly, if the gain controlsignal is above a predefined value (e.g. GC≧27) corresponding to arelatively high gain setting of the variable amplifier and thus arelatively weak input signal), the tuning of the receiving antenna isimproved (e.g. in one or more steps) to increase the signal strength.

The problem is particularly relevant in a system comprising a portable,battery driven receiver with restrictive requirements to powerconsumption (including a low battery voltage and a low batterycapacity). An example of such a system is an audio system comprising a(possibly portable) wireless transmitter and a listening devicecomprising a wireless receiver, in particular wherein the communicationlink between transmitter and receiver is based on inductivecommunication. Such system, based on an inductive communication link,has the potential of providing a relatively low power consumption. Thesystem, on the other hand, is also sensitive to the distance L betweentransmitter and receiver due to the 1/L³ dependence of the fieldstrength and thus prone to saturation problems, when the two devicescome close to each other. In this case a system according to the presentdisclosure is particularly valuable.

FIG. 1 shows an embodiment of a portable electronic device according tothe present application. The portable electronic device of FIG. 1, e.g.a listening device, e.g. a hearing instrument, comprises a wirelessreceiver unit for receiving a wireless signal from a transmittingdevice, the wireless receiver unit comprising an antenna (101) forreceiving an electromagnetic signal and providing a received electricinput signal (102), and a receiver (103) for providing a recoveredelectric signal from the received electric input signal, and animpedance matching circuit (104) for matching the electric impedance ofthe antenna (101) to the receiver (103). The receiver comprises a gainstage comprising a first, fixed (pre-amplifying) gain stage (105) and asecond, variable gain stage (106). The fixed gain stage (105) amplifiesan input signal (here received electric input signal 102) with a fixedgain value and provides an amplified output signal (107). The variablegain of the second stage (106) allows the receiver itself to set thegain to an appropriate value, ensuring the optimum signal level for thesucceeding receiver or processing circuits (here signal processing unit108). The variable gain stage, in the form of Automatic Gain Controlunit (106), is adapted for automatically determining an AGC-gain value(also referred to as control signal 109) for application to an AGC-inputsignal (107) to provide an appropriate signal level of the recoveredelectric signal (110) when the level of said AGC input signal is in arange between a minimum signal level and a maximum signal levelcorresponding to maximum and minimum AGC-gain values, respectively. Theportable electronic device further comprises a control unit (here signalprocessing unit 108) receiving the AGC-gain value (109) and providing animpedance matching control signal (111) to the impedance matchingcircuit (104)). The control unit (108) is adapted to change theimpedance matching of the antenna (101) to the receiver (103) based onthe AGC-gain value GC. In an embodiment, the fixed gain stage (105) isomitted. Typically, the gain stage (e.g. the AGC-unit) is only capableof amplifying an input signal, not to attenuate the signal (or not toattenuate it sufficiently, in order to avoid saturation of the gainstage).

FIG. 2 shows two embodiments of an antenna and a variable impedancematching circuit. The antenna (101 in FIG. 1) is shown as an inductivecoil with inductance (L_(A)). The impedance matching circuit (104 inFIG. 1) is shown as a variable capacitance (C, FIG. 2 a) and a variableresistance (R, FIG. 2 b), respectively. In both cases, the value of theimpedance can be controlled by an impedance matching control signal(111) (provided by control unit 108 in FIG. 1) from a minimum value to amaximum value, preferably in a number of steps. Preferably, the minimumand maximum values are determined with a view to the antenna (101)impedance (L_(A)) and the receiver (103) input impedance. Alternatively,or additionally the inductance L_(A) may be variable.

FIG. 3 shows two embodiments of a variable impedance matching circuit.FIG. 3 a schematically illustrates an embodiment comprising a number ofparallel components (e.g. resistors or capacitors or inductance coils,here four values are indicated, 1, 2, 4, 8) having different impedances,e.g. increasing values, e.g. mutually scaled as indicated by the numbers1, 2, 4, 8. One or more of the impedances (1, 2, 4, 8) can be switchedin the signal path coupling electric input signal 102 from the antenna101 of FIG. 1 to ground by switches S1, S2, S4, S8 controlled byimpedance matching control signal IMC 111 (generated by control unit(108) in FIG. 1). Similarly, FIG. 3 b schematically illustrates anembodiment comprising a number of serially coupled components (e.g.resistors or capacitors or inductors, here four values are indicated, 1,2, 4, 8) having different impedances, e.g. increasing values, e.g.mutually scaled as indicated by the numbers 1, 2, 4, 8. Thereby theimpedance of the antenna can be matched (or de-matched) to the receiverinput impedance in a number of steps.

FIG. 4 shows a use scenario for a communication system according to thepresent application. FIG. 4 shows an application scenario of anembodiment of a portable listening system according to the presentapplication comprising a pair of listening devices, in the form or abinaural hearing aid system comprising first and second hearinginstruments (HI-1, HI-2), and an audio gateway device (AG), wherein theaudio gateway device comprises an audio selection device adapted forreceiving a multitude of audio signals (here shown from an entertainmentdevice, e.g. a TV 52, a telephone apparatus, e.g. a mobile telephone 51,a computer, e.g. a PC 53, and an external microphone xMIC for picking upsounds xIS from the environment, e.g. the voice of another person). Inthe embodiment of FIG. 4, the microphone 11 of the audio gateway deviceis adapted for picking up the user's own voice 31 and capable of beingconnected to one or more of the external audio sources 51, 52, 53, xMICvia wireless links 6, here in the form of digital transmission linksaccording to the Bluetooth standard as indicated by the Bluetoothtransceiver 14 (BT-Tx-Rx) in the audio gateway device 1. The audiosources and the audio gateway device may be paired using the buttonBT-pair. The links may alternatively be implemented in any otherconvenient wireless and/or wired manner, and according to anyappropriate modulation type or transmission standard, possibly differentfor different audio sources. Other audio sources than the ones shown inFIG. 4 may be connectable to the audio gateway, e.g. an audio deliverydevice (such as a music player or the like). The intended mode ofoperation of the listening system can be selected by the user via modeselection buttons Mode1 and Mode2. The audio gateway device may furtherhave the function of a remote control of the listening device, e.g. forchanging program or operating parameters (e.g. volume, cf. Vol-button)in the listening device.

The hearing instruments (HI-1, HI-2) are adapted for being mounted atthe left and right ears, respectively, of a user (U). Each hearinginstrument of the embodiment of FIG. 4 comprises a wireless transceiverfor establishing a link to the audio gateway device (AG) (and/or aremote control device), here indicated to be based on inductivecommunication (I-Rx). The transceiver (at least) comprises an inductivereceiver (i.e. an inductive coil, which is inductively coupled to acorresponding coil in a transceiver (I-Tx) of the audio gateway deviceAG), which is adapted to receive a wireless signal (e.g. comprising anaudio signal and/or control signals) from the audio gateway device(either as a baseband signal or as a modulated (analogue or digital)signal, and in the latter case to extract the audio signal from themodulated signal). The hearing instruments (HI-1, HI-2) each comprisesan antenna, an impedance matching circuit, a receiver and a control unitas described in connection with FIG. 1 above. Thereby an increasedflexibility in the location of the audio gateway device (AG) relative tothe hearing instruments (HI-1, HI-2) is provided.

The inductive link 41 between the audio gateway device and the hearinginstruments is indicated to be one-way, but may alternatively be two-way(e.g. to be able to exchange control signals between transmitting (AG)and receiving (HI-1, HI-2) device, e.g. to agree on an appropriatetransmission channel). Alternatively or additionally, the hearinginstruments (and/or the audio gateway device) may be adapted to receivean audio signal from a telecoil (T-coil) in the environment of thedevice.

The hearing instruments (HI-1, HI-2) each comprise a selector/mixer unit(SEL/MIX) for selecting either of an input audio signal from amicrophone of the instrument or the input signal from the wirelessreceiver unit (I-Rx) or a mixture thereof, providing as an output aresulting input signal. In an embodiment, the selector/mixer unit can becontrolled by the user via the user interface (UI).

The audio gateway device (AG) is shown to be carried around the neck ofthe user (U) in a neck-strap 42. The neck-strap 42 may have the combinedfunction of a carrying strap and a loop antenna into which the audiosignal from the audio gateway device is fed for better inductivecoupling to the inductive transceiver of the listening device. An audioselection device, which may be modified and used according to thepresent invention is e.g. described in EP 1 460 769 A1, EP 1 981 253 A1and in WO 2009/135872 A1.

FIG. 5 illustrates an example of the effect on dynamic range of a signalreceived by an antenna by the application of a variable impedancematching circuit (104 in FIG. 1) according to the present disclosure.The ‘Normal dynamic range’ between a minimum signal strength (SS) level,SS_(min), and a maximum signal strength level, SS_(maxN), of a gainstage comprising an AGC unit is illustrated in the lower part of FIG. 5next to the ‘Extended dynamic range’ of the same gain stage comprisingan impedance matching circuit controllable according to the presentdisclosure. The top graph of FIG. 5 illustrates a schematic example ofthe variation of gain G_(A) of an AGC unit with increasing signalstrength (input level, SS in [dB]) of the input signal to the AGC unit(e.g. received from the antenna). The gain decreases from a maximumvalue (G_(Amax)) to a minimum value (G_(Amin)). When the signal strengthof the input signal to the AGC increases beyond SS_(maxN) (correspondingto the upper level of the normal dynamic range and a gain of G_(Amin) ofthe AGC unit) G_(A) cannot be lowered further. A gain stage without thevariable impedance matching circuit according to the present disclosure(to attenuate the input signal to the gain stage from the antenna) wouldbe saturated for antenna signal strengths larger than SS_(maxN).According to the present disclosure the variable impedance matchingcircuit may increase the normal dynamic range (S_(min) to SS_(maxN)) toan extended dynamic range (S_(min) to SS_(maxX)) by decreasing thedegree of match of the impedance matching circuit between the antennaand the receiver, thereby decreasing the input signal from the antennato the gain stage as illustrated in the bottom graph of FIG. 5. Therebythe antenna signal is allowed a larger dynamic range, while still beingappropriately handled by the gain stage. The gain (attenuation) G_(Z) ofthe impedance matching circuit is in the example of FIG. 5 shown to bevariable between a maximum value (G_(Zmax), here 1) and a minimum valueG_(Zmin), e.g. 0.01 (or larger). In an embodiment, the maximum valueG_(Zmax) is smaller than or equal to 1, e.g. in the range between 0.5and 1. In an embodiment, the maximum value G_(Amax) of the gain of theAGC of the gain stage is 10⁵. In an embodiment, the minimum valueG_(Amin) of the gain of the AGC of the gain stage is equal to 1.Alternatively the minimum value G_(Amin) may be larger than 1 (e.g.larger than or equal to 100) or smaller than 1 (e.g. smaller than orequal to 0.01). In case, the gain stage comprises a first, fixed(pre-amplifying) gain stage, the minimum gain G_(Amin) is typicallydetermined by the fixed gain of such stage. In the example of FIG. 5,top graph, the variation of the gain G_(A) of the AGC unit with inputsignal strength is shown to be linear on a logarithmic scale of thesignal strength [dB]. This need not be the case. Any other functionaldependence providing a decreasing gain G with increasing signal SSstrength may be possible. The same is the case for the gain(attenuation) G_(Z) of the impedance matching circuit illustrated in thebottom graph of FIG. 5.

The invention is defined by the features of the independent claim(s).Preferred embodiments are defined in the dependent claims. Any referencenumerals in the claims are intended to be non-limiting for their scope.

Some preferred embodiments have been shown in the foregoing, but itshould be stressed that the invention is not limited to these, but maybe embodied in other ways within the subject-matter defined in thefollowing claims.

REFERENCES

-   -   EP 2 211 579 A1 (OTICON)    -   [Schaub; 2008] Arthur Schaub, Digital hearing Aids, Thieme        Medical. Pub., 2008.    -   WO 03/081947 A1 (OTICON)    -   U.S. Pat. No. 5,144,675 (ETYMOTIC)    -   EP 1 460 769 A1 (PHONAK)    -   EP 1 981 253 A1 (OTICON)    -   WO 2009/135872 A1 (OTICON)    -   US 2009/0130991 A1 (BROADCOM CORPORATION)    -   US 2004/0080372 A1 (FARADAY TECH CORP)

The invention claimed is:
 1. A portable electronic device, comprising: awireless receiver unit for receiving a wireless signal from atransmitting device, the wireless receiver unit including an antenna forreceiving an electromagnetic signal and providing a received electricinput signal, and a receiver for providing a recovered electric signalfrom the received electric input signal; and an impedance matchingcircuit for matching an electric impedance of the antenna to thereceiver, wherein the receiver includes a gain stage, the gain stageincluding a variable gain stage in the form of an Automatic Gain Controlunit for automatically determining an AGC-gain value for application toan AGC-input signal to provide an appropriate signal level of therecovered electric signal when the level of said AGC-input signal is ina range between a predetermined minimum signal level and a predeterminedmaximum signal level corresponding to maximum and minimum AGC-gainvalues, respectively, the gain stage is configured to amplify thereceived electric input signal, but not to attenuate the receivedelectric input signal, the portable electronic device further includes acontrol unit receiving said AGC-gain value and providing an impedancematching control signal depending on said AGC-gain value to saidimpedance matching circuit, the control unit is configured to change theimpedance matching of the antenna to the receiver by supplying theimpedance matching control signal to the impedance matching circuit, andthe control unit is further configured to decrease the impedancematching of the impedance matching circuit when said AGC-gain value isbelow a predefined minimum threshold AGC-gain value, thereby attenuatingthe received electric input signal when its level is larger than anupper limit of a dynamic range of the gain stage.
 2. A portableelectronic device according to claim 1 wherein the control unit isadapted to increase the impedance matching of the impedance matchingcircuit when said AGC-gain value is above a predefined maximum thresholdAGC-gain value.
 3. A portable electronic device according to claim 1wherein the Automatic Gain Control unit is adapted to provide saidAGC-gain values in steps between a minimum and a maximum value.
 4. Aportable electronic device according to claim 1 wherein the impedancematching circuit comprises one or more of a variable capacitance, avariable resistance and a variable inductance.
 5. A portable electronicdevice according to claim 1, wherein the antenna comprises a coil.
 6. Aportable electronic device according to claim 5, wherein the antennacomprises a coil, and the coil of the antenna is part of an inductivelink based on inductive coupling between an antenna coil of thetransmitting device and said coil of the antenna.
 7. A portableelectronic device according to claim 1, wherein the antenna comprises apatch.
 8. A portable electronic device according to claim 1 adapted toprovide that the change of the impedance matching of the antenna to thereceiver is performed in one or more steps controlled by said controlsignal from the control unit.
 9. A portable electronic device accordingto any one of claims 1 and 3-8, wherein the gain stage further comprisesa fixed gain stage.
 10. A portable electronic device according to claim1, comprising a hearing aid.
 11. A communication system comprising aportable electronic device according to claim 1 and a transmittingdevice, the portable electronic device and the transmitting device beingadapted to establish a wireless link between them at least allowing asignal to be transmitted from the transmitting device to the portableelectronic device.
 12. A communication system according to claim 11,wherein the wireless link is based on inductive coupling betweenrespective antenna coils of the transmitting device and the portableelectronic device.
 13. A communication system according to claim 11,wherein the transmitting device is one of an audio gateway device, anentertainment device, and a listening device, and wherein the system isconfigured to transmit and receive audio via the wireless link.
 14. Acommunication system according to claim 11, further comprising a firstlistening device, wherein the portable electronic device is a secondlistening device, and the first and second listening devices areconfigured to implement a binaural listening system.
 15. A communicationsystem according to claim 14, wherein the binaural listening system is abinaural hearing aid system.
 16. A method of operating a wirelessreceiver unit for receiving a wireless signal from a transmittingdevice, wherein the wireless receiver unit includes an antenna forreceiving an electromagnetic signal and providing a received electricinput signal, a receiver for providing a recovered electric signal fromthe received electric input signal, and an impedance matching circuitfor matching an electric impedance of the antenna to the receiver, themethod comprising: automatically determining an AGC-gain value in thereceiver for application to an AGC-input signal to provide amplificationbut not attenuation of the recovered electric signal when the level ofsaid AGC-input signal is in a range between a predetermined minimumsignal level and a predetermined maximum signal level corresponding tomaximum and minimum AGC-gain values, respectively; and changing theimpedance matching of the antenna to the receiver in the impedancematching circuit based on the AGC-gain value, wherein the changing theimpedance matching includes decreasing the impedance matching of theantenna to the receiver when said AGC-gain value is below a predefinedminimum threshold AGC-gain value, thereby attenuating the receivedelectric input signal when its level is larger than an upper limit of adynamic range of a gain stage of the wireless receiver unit.
 17. Atangible computer-readable medium storing a computer program comprisingprogram code means for causing a data processing system to perform thesteps of the method of claim 16, when said computer program is executedon the data processing system.